The embodiment relates to a diagnostic apparatus connected to an inverter for an electric vehicle. More particularly, the embodiment relates to an apparatus for diagnosing a relay contact, which is installed at a power line connected to a motor controller to diagnose fusion of a high voltage relay contact that switches a main power source on or off, and a method thereof.
An inverter serving as a motor controller employed in an eco-friendly vehicle is an electric/electronic sub-assembly (ESA) to convert high-voltage DC power into AC power or DC power for the purpose of controlling a motor. The inverter is a main component serving as an electric driving device of a vehicle.
In such an eco-friendly vehicle, a high-voltage relay is connected to a power line for each motor and each motor controller including an inverter such that the high-voltage relay switches on or off of the battery serving as a main power source. The high-voltage relay is equipped with an emergency operation control function for driving a vehicle through the motor and the power cutoff function even when an emergency operation is performed caused by the failure of two motors and two motor controller from among three motors and three motor controllers.
That is, when dielectric breakdown or a problem occurs in an IGBT (Insulated Gate Bipolar Transistor), which is an inverter included in the motor controller, due to an overvoltage or overcurrent while the vehicle is being operated, the high-voltage relay connected to the power line cuts off the power being supplied to the corresponding motor and motor controller and performs an emergency operation using other motors and motor controllers which remain in a normal state.
Since large current flows bilaterally through the high-voltage relay which controls the power supply to the motor and the motor controller, the possibility of the fusion of the high-voltage relay is very high due to a temperature increase and a fault component. Since it is impossible in the fusion state to cut off the power supply to the motor and the motor controller subject to troubles, the counter electromotive force generated due to the rotation of the motor having the trouble exerts effect on other normal motors and motor controller so that a continuous current flow occurs.
FIG. 1 is a flowchart illustrating a method of diagnosing a relay contact point according to the related art which is disclosed in Korean Patent Application No. 10-2009-0118728.
Referring to FIG. 1, in a state that a fuel cell vehicle is operated in step S101, it is determined in step S102 whether a fuel cell stack is normally shut down in response to a stop of the vehicle.
In step S102, if the fuel cell stack is normally shut down, a main controller primarily turns off the first to third relays Ry1, Ry2 and Ry3 such that the output powers of the fuel cell stack and the super capacitor are primarily shut down and then turns off the fourth relay which is a high-voltage relay, so that the power supply to the motor controller is blocked.
In this case, although a periphery complementary apparatus blocks the hydrogen supplied to the anode of the fuel cell stack and supplies oxygen to remove residual hydrogen, since power is not normally supplied, energy of an internal capacitor C is used to drive the periphery complementary apparatus so that a voltage variation occurs.
In addition, if the power supplied to the motor controller is shut off as the fourth relay Ry4 is turned off, a voltage drop of a capacitor C1 is constantly caused by an internal resistance R.
Thus, a main controller detects a voltage variation (Δ(LDC) of the internal capacitor C in step S103, detects a voltage variation (Δ(MCU)) of the internal capacitor C1 in step S104, and then compares the two detected voltage variation values with each other in step S105.
It is determined in step S106 whether the detected main voltage values are equal to each other. If the voltage values are not equal to each other, it is determined in step S109 that the high-voltage relay Ry4 connected to the power line is normal.
However, if the voltage values are equal to each other, it is determined in step S107 that the periphery complementary apparatus uses the voltage of the internal capacitor C1 of the motor controller due to the fusion of the high-voltage relay Ry4 connected to the power line of the motor controller.
As described above, if it is determined that the fusion of the high-voltage relay Ry4 connected to the power line occurs, a diagnostic code is stored in a memory such that a driver can rapidly exchange the relay.
The method of diagnosing a relay contact according to the related art is performed when the ignition is shut down through a separated electric component (LDC; low voltage DC-DC converter) in order to detect a fusion of a relay.
However, the method of diagnosing a relay contact according to the related art requires the connection with the separated electric component (LDC) and is performed upon the shutdown. When the separated electric component is out of order upon the shutdown, the relay diagnosis is not normally performed, so that a driver may be subject to the dangerous situation.